Microwave oscillator

Abstract

An improvement in a microwave oscillator using a GaAs FET as the active element is shown to include a phase detector responsive to a portion of the positive feedback signals applied to a resonator having a high Q and to a portion of the signals out of the GaAs FET, shifted by 90°, to obtain signals to degenerate noise internally formed in the GaAs FET.

What is claimed is: 
     
       1. In a microwave oscillator using a GaAs FET as the active element, such oscillator including a resonator with a high Q to provide positive feedback and to reduce FM noise, the improvement comprising: (a) phase detector means, responsive to signals out of the GaAs FET shifted by 90° and to a portion of the positive feedback signals, for providing signals representative of low frequency noise arising within the GaAs FET; and   (b) means for feeding back the signals out of the phase detector to degenerate such low frequency noise.   
     
     
       2. In a microwave oscillator using a GaAs FET as the active element, such FET having a gate electrode, a drain electrode and a grounded source electrode with a resonator having a high Q in circuit between the drain electrode and the gate electrode to provide positive feedback and to determine the frequency of oscillation, the improvement comprising: (a) first means for dividing the signals out of the drain electrode into at least a first and a second path;   (b) a circulator disposed in circuit in the first path, such circulator having a first, second and third port, the first port receiving signals from the first means, the second port being connected to the resonator and the third port passing therefrom signals reflected from the resonator;   (c) a phase detector having a first and a second input terminal and an output terminal, the first input terminal receiving the signals out of the third port of the circulator;   (d) a 90° phase shifter disposed in the second path between the first means and the second input terminal of the phase detector; and,   (e) second means, connected in circuit between the output terminal of the phase detector and the gate electrode of the GaAs FET, for applying such electrode signals to degenerate internally formed noise.